The present invention relates to a manufacturing process for a structure of a semiconductor on insulator (SeOI) having reduced electrical losses. It also relates to such a structure.
The invention focuses on the general context of manufacturing a structure of semiconductor on insulator type (SOI) by the SmartCut™ process. This process is described in detail, for example, in U.S. Pat. No. 5,374,564. A structure of this type generally comprises a support layer, typically made of silicon monocrystalline having high resistivity, an insulating oxide layer, and a thin layer of semiconductor material. This thin layer is designed to take up components, typically electronic components.
In particular, in applications in which use is made of radio-frequencies, for example in the field of radiophony, part of the emitted waves can be absorbed by the support substrate, despite the presence of the insulating layer, resulting in electrical losses. To combat this difficulty, it has been proposed to boost resistivity of the support substrate to over 500 Ω·cm, or even over a few thousand Ohms·cm, though this does not prove to be sufficient. It was then proposed to deposit on the upper face of the support substrate (that is, the one receiving the insulating layer and the thin layer), a layer of material whereof the density of charge-carrier traps is high. A polycrystalline silicon layer is adapted in particular to ensure this function. Its structure is formed by a multitude of crystalline grains having defective boundaries (grain joint) forming traps, which makes the ensemble particularly low-conductive. This reduces leakage currents and losses in resistivity at the level of the support substrate.
The technique to achieve the foregoing structure includes depositing a polycrystalline silicon layer on the support substrate, then applying the usual steps of the SmartCut™ process. This type of method is described in particular in US Patent Application 2007/0032042. When conducting tests on resulting structures which would exhibit high resistivity according to the teachings of that application, however, it was found that the technique in question did not reduce electrical losses satisfactorily. Thus, there remains a need for different solutions to this problem, and these are now provided by the present invention.